The present invention relates to wire rope and, more particularly, to plastic encapsulated wire rope having spacer strands between its central core strand and surrounding outer strands.
Plastic encapsulated wire rope, such as disclosed in U.S. Pat. No. 3,824,777, has been demonstrated to have properties such as tensile strength, fatigue life and corrosion resistance superior to those of equal size bare wire rope. Such improved properties are derived from the separation of the core strand from the outer strands and the outer strands from each other by the thermoplastic material. Suitable themoplastics include polypropylene, polyurethane, polyethylene, nylon, tetrafluroethylene or polyvinylchloride. Also useful are elastomers such as butyl or nitrile rubber. Such a coating reduces or eliminates such core to strand and strand to strand contact and abrasion when the rope is in service. Further, the coating traps any desired lubricant such as petrolatum within the strands and resists the ingress of abrasive or corrosive elements into the rope.
However, it is desirable to achieve strand gap or interstice balance in the manufacture of such plastic encapsulated wire rope. Such gap balance insures the equal load sharing by the strands of the rope and also assures the spacing between strands is filled with plastic. One method of such gap control during rope manufacture is set forth in U.S. Pat. No. 3,824,777, wherein a strand gap controller die is utilized to equally separate rope strands during the injection of the plastic.
Another spacing control method is disclosed in U.K. patent application No. 2,090,305 A, wherein a filler element of thermoplastic containing a reinforcing core is placed independently in the interstice. The presence of such independent thermoplastic element would prohibit the introduction of a flowable thermoplastic into the wire rope.
It is an object of the present invention to provide an encapsulated wire rope having uniform strand gaps and a method of making such rope.